1. Field of the Invention
The present invention relates generally to the rerighting of a capsized craft and more specifically to a method and apparatus for self-righting a multihulled waterborne craft.
2. Discussion of the Prior Art
Multihulled craft are extremely stable seagoing platforms and have been utilized for centuries for extended ocean passages (see for example the Poynesian travels to Hawaii in crude but seaworthy catamaran craft). However, the separation of the hulls which provide the multi-hull stability provide similar stability when the craft is capsized (upside down), making it extremely difficult to re-right the craft. Whereas the typical lead keel monohull sailboat will re-right itself due to the location of the ballast in the craft, the same is not true with multihulled craft because the ballast contained will not overcome the stabilizing effect of the multiple hulls when these hulls are uspside down and have a volume of air located thereunder.
Although a multi-hulled craft which has been capsized remains a very stable plarform and can be lived on or in for numerous weeks while awaiting rescue, it would be advantageous to be able to re-right the craft at sea effecting a self rescue for the occupants and the craft. There have been proposed a number of methods for re-righting capsized multiple hull vessel, many of which utilize the vessel's mast to provide leverage with which to overcome the stability imparted by the outrigger or buoyant hulls. Essentially a float is provided in the form of a life raft or other inflatable device which can be winched "down" to the top of the mast. The greater moment arm of a float at the end of the mast as opposed to the buoyancy of the hull displaced from the base of the mast provides a sufficient moment arm to rotate the craft approximately 90.degree. and then by either floating or pumping out one of the buoyant hulls the remaining righting moment is provided to bring the boat to its normal condition. There are numerous variations upon the theme which uses the mast to provide an extremely long moment arm for self-righting of a multi-hull vessel. However, all of these methdos suffer from the simple defect that if the mast is no longer in place after capsize there will be no way for the craft to be righted. A review of actual capsizes proves that the mast is not always present or has been damaged to the extent that it cannot be used to provide the necessary overturning moment.
Another method makes the use of an A-frame or a guyed pole located near one end of the craft with a water bag suspended therefrom. As water is pumped into the water bag suspended just above the surface, the end of the boat on which the A-frame or pole is located is depressed into the water. As the bag is filled with water and the end of the boat is depressed, the A-frame or pole is winched up so as to keep the bag above the water's surface. This process will continue until the boat is pulled past the 90.degree. point, at which point it continues to overturn until it is almost upright and any remaining water inside the craft can be bailed or drained out. Variations upon this theme require the flooding of a portion of the hull in a multi-hulled craft of external flotation devices in the form of a life raft or dingy to provide an additional overturning moment.
Common to all of these methods is the requirement of a considerable amount of crew effort which may not be available after capsize and in difficult sea conditions. Further, these methods are dependent upon a number of mechanical devices which could fail or be lost during capsize, rendering the entire system inoperative. For these reasons, the "real world" usefulness of these methods is doubtful. There are additional righting methods for multihulled craft in which a watertight bulkhead is provided in the craft and, after a forward compartment is flooded, an air bag is inflated amid ships under the craft and is winched in a more forward position as the craft begins to right. A variation upon this method is that disclosed in U.S. Pat. No. 4,227,474 to Ullrich which discloses a watertight cabin at the aft portion of a catamaran with floodable chambers in the bow. The bow chambers are flooded and the craft rotates approximately 130.degree. from the initial capsized position. At this point compressed air is utilized to force water out of the floodable bow chambers completing the re-reghting and additional water in the main hulls is then pumped out by the crew. Problems with both of the above methods arise in that it requires that the integrity of a water-tight compartment (either the aft cabin in Ullrich or the air bags) be maintained and in addition a compressed air source must be maintained in a fully charged state.
Thus, all previous self-righting systems required that the mast be intact and structurally sound after capsize, requires intense crew efforts after capsize, or depends upon watertight compartments or inflatable bags in combination with compressed air inflating mechanisms in order to effect the righting action.
In an article entitled "Capsize Recovery For Trimarans" by Derek Kelsall published in the November/December 1982 issue of MultiHulls magazine, there is disclosed the use of extremely large air bags on which to float almost the entire weight of a trimaran, such that when one outer hull is submerged the crew assisting can lift the mast and provide enogh of a righting moment to re-right a trimaran without the main hull becoming flooded. Of course this requires a substantial additional structure in the form of air bags, and their inflating mechanisms as well as crew aid in positioning the air bags, lifting the mast, etc. While such a re-righiting system is certainly feasible, it is still dependent upon the crew being healthy and available, the air bags and their inflation system being intact and and operable and would seem to require substantial effort to initiate the operation.